These chiles are thought to be related to the cayenne pepper, and are named for the woody stem attached to them. Chiles de arbol remain a vibrant red when dried, unlike other varieties, and are quite hot (about an 8 on a scale of 1-10). Add a few dried chiles to Thai curries, stir fries and chili for a kick of heat. They can be found in the produce section of most markets.
Choose chiles that are shiny and firm pods with strong, uniform color. They should feel dense and heavy for their size; good examples of even the very smallest ones will feel heavier. Avoid chiles that are flaccid, wrinkled, bruised, blemished, or discolored.